Project Abstract The long-term goal of this work is to non-invasively evaluate regional changes in foot tissue perfusion following lower extremity revascularization to better predict efficacy of targeted treatment and future rates of wound healing and limb salvage. Peripheral vascular disease (PVD) is an atherosclerotic disease of the lower limbs that affects 8 to 10 million Americans, and is more prevalent and progresses more quickly in patients with diabetes mellitus (DM). In addition to macrovascular complications, DM patients commonly present with microvascular disease of the lower extremities, which may contribute to high rates of foot ulceration, limb amputation, and poor treatment outcomes that exist in the setting of DM. Current imaging tools have limitations for assessing underlying microvascular disease and there is no standard non-invasive approach to evaluate changes in microvascular perfusion in three-dimensional (3D) vascular territories of the feet, or angiosomes, following medical treatment in PVD patients. We propose a novel approach for evaluating angiosome microvascular perfusion under resting conditions in DM patients with critical limb ischemia (CLI) who are undergoing revascularization. Using hybrid SPECT/CT imaging, we will evaluate microvascular perfusion within 3D angiosomes of the foot that are targeted for direct revascularization due to pre-existing non-healing wounds, and relate changes in relative and absolute angiosome perfusion to rates of wound healing and limb salvage. The central hypothesis of this work is that radiotracer-based imaging of microvascular perfusion can detect sensitive changes in underlying pathophysiology of the foot in specific vascular territories, which can assist clinicians with targeted revascularization while also predicting treatment efficacy and limb salvage outcomes. In Aim 1 we will quantify relative changes in resting microvascular perfusion within 3D angiosomes of the foot using SPECT/CT imaging to evaluate revascularization procedures targeted at non-healing wounds in DM patients with CLI, and relate changes in angiosome perfusion to wound healing and limb salvage outcomes. Aim 2 will validate the utility of dynamic SPECT/CT imaging for quantifying serial changes in absolute skeletal muscle perfusion in a large animal model of peripheral artery occlusion. Finally, Aim 3 will translate dynamic SPECT/CT imaging into patients to evaluate the repeatability of this approach and to assess the value of absolute quantitative perfusion in 3D angiosomes in DM patients undergoing revascularization. We believe that radiotracer-based imaging will allow for high sensitivity detection of impaired foot tissue perfusion under resting conditions at baseline and following revascularization. Therefore, this imaging approach may help to identify patients at risk for wound progression or limb loss and assist in predicting treatment outcomes in PVD patients.